From "Houben-Weyl, Methoden der Organishcen Chemie, IX", page 653 it is known to prepare azidosulphonylbenzenes either by reacting chlorosulphonylbenzenes with sodiumazide or by reacting hydrazinosulphonylbenzenes with sodiumnitrite. It is further known from J. Chem. Soc. (C), 1968, pages 11-16, to prepare azidosulphonylbenzoic acids by reacting the chlorosulphonylbenzoic acids with hydrazine hydrate in ethanol or dioxan at a low temperature, e.g. 0.degree. C. After cautions acidification and generally recrystallization the corresponding hydrazinosulphonyl benzoic acids are obtained as crystals, which decompose at their melting point. The hydrazinosulphonylbenzoic acids are converted into the corresponding azidosulphonylbenzoic acids. Disadvantages in the process for preparing azidosulphonylbenzoic acids are the use of an organic solvent, e.g. ethanol or dioxan, the isolation of the hydrazide intermediate with recrystallization, the two step process and molar excess of hydrazine. A disadvantage of the use of sodiumazide is the limited availability and the expensiveness of the sodiumazide.